It's probably one of these:

callus

Callus

(n.) Same as Callosity

(n.) The material of repair in fractures of bone; a substance exuded at the site of fracture, which is at first soft or cartilaginous in consistence, but is ultimately converted into true bone and unites the fragments into a single piece.

(n.) The new formation over the end of a cutting, before it puts out rootlets.